Polyaxial bone screw with multi-part shank retainer and pressure insert

ABSTRACT

A polyaxial bone screw assembly includes a threaded shank body having an upper portion, a receiver, a compression insert and an articulation structure made from at least two discrete pieces. The shank upper portion cooperates with the compression insert to place the retainer in frictional engagement with the receiver. The geometry of the retainer structure pieces corresponds and cooperates with the external geometry of the shank upper portion to frictionally envelope the retainer structure between the capture structure and an internal surface defining a cavity of the receiver.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/080,202, filed Apr. 1, 2008 that was a continuation-in-part of U.S.patent application Ser. No. 11/281,818 filed Nov. 17, 2005, now U.S.Pat. No. 7,625,396, issued Dec. 1, 2009 that claimed the benefit of U.S.Provisional Application No. 60/630,478 filed Nov. 23, 2004, all of whichare incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention is directed to polyaxial bone screws for use inbone surgery, particularly spinal surgery and particularly to suchscrews that have pressure inserts.

Bone screws are utilized in many types of spinal surgery in order tosecure various implants to vertebrae along the spinal column for thepurpose of stabilizing and/or adjusting spinal alignment. Although bothclosed-ended and open-ended bone screws are known, open-ended screws areparticularly well suited for connections to rods and connector arms,because such rods or arms do not need to be passed through a closedbore, but rather can be laid or urged into an open channel within areceiver or head of such a screw.

Typical open-ended bone screws include a threaded shank with a pair ofparallel projecting branches or arms which form a yoke with a U-shapedslot or channel to receive a rod. Hooks and other types of connectors,as are used in spinal fixation techniques, may also include open endsfor receiving rods or portions of other structure.

A common mechanism for providing vertebral support is to implant bonescrews into certain bones which then in turn support a longitudinalstructure such as a rod, or are supported by such a rod. Bone screws ofthis type may have a fixed head or receiver relative to a shank thereof.In the fixed bone screws, the rod receiver head cannot be moved relativeto the shank and the rod must be favorably positioned in order for it tobe placed within the receiver head. This is sometimes very difficult orimpossible to do. Therefore, polyaxial bone screws are commonlypreferred.

Open-ended polyaxial bone screws allow rotation of the head or receiverabout the shank until a desired rotational position of the head isachieved relative to the shank. Thereafter, a rod can be inserted intothe head or receiver and eventually the receiver is locked or fixed in aparticular position relative to the shank. During the rod implantationprocess it is desirable to utilize bone screws or other bone anchorsthat have components, or inserts that remain within the bone screw andfurther remain properly aligned during what is sometimes a very lengthy,difficult procedure.

SUMMARY OF THE INVENTION

A polyaxial bone screw assembly according to the invention includes ashank having an upper portion and a body for fixation to a bone; a heador receiver defining an open channel; a multi-part or piece retainer forpivotally holding the upper portion in the receiver; and at least onecompression insert spaced above and apart from the retainer structure.The shank upper portion is bottom or up-loadable into the receiver,cooperates with the retainer, and has a top end which extends above atop surface of the retainer; the retainer having polyaxial motion withrespect to the receiver; and the retainer including more than onediscrete piece, each piece frictionally engageable with the shank upperportion, slidably engageable with the receiver and located between theshank upper portion and the receiver and spaced below the insert. Inembodiments wherein the compression insert includes arms defining aU-shaped channel, the receiver further includes structure cooperatingwith the compression insert that hold such insert in a desired positionor alignment within the receiver, such as spring tabs that project intothe receiver cavity either upwardly or downwardly and into depressionsor grooves formed in the insert arms.

OBJECTS AND ADVANTAGES OF THE INVENTION

Therefore, it is an object of the present invention to provide apparatusand methods directed to a shank that is up or down loadable into acavity in a receiver of the screw and that utilizes a retainer that maybe also uploaded or downloaded into the cavity. Another object of theinvention is to provide discrete retainer parts or segments configuredto fixedly engage the shank upper portion and slidably engage thereceiver so as to polyaxially articulate with the receiver until thereceiver is fixed relative to the shank, when a desired configuration isacquired, while therebetween holding the shank upper portion in a spacedrelation from the receiver. Furthermore, it is an object of theinvention to provide a lightweight, low profile polyaxial bone screwthat assembles in such a manner that the components cooperate to createan overall structure that provides an even gripping of a shank capturestructure to the receiver. Furthermore, it is an object of the inventionto provide apparatus and methods that are easy to use and especiallyadapted for the intended use thereof and wherein the tools arecomparatively inexpensive to produce.

Other objects and advantages of this invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention.

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention and illustrate variousobjects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a polyaxial bone screwassembly according to the present invention including a shank, areceiver, a two-piece retainer and a compression insert and furthershown with a longitudinal connecting member and a closure top.

FIG. 2 is an enlarged and partial front elevational view of the shank ofFIG. 1.

FIG. 3 is an enlarged top plan view of the shank of FIG. 1.

FIG. 4 is an enlarged top plan view of the retainer of FIG. 1.

FIG. 5 is an enlarged cross-sectional view taken along the line 5-5 ofFIG. 4.

FIG. 6 is an enlarged cross-sectional view of the receiver, taken alongthe line 6-6 of FIG. 1 and the two-piece retainer as shown in thecross-sectional view of FIG. 5 in a method of assembly according to theinvention.

FIG. 7 is an enlarged cross-sectional view of the receiver, taken alongthe line 6-6 of FIG. 1, an enlarged and partial cross-sectional view ofthe shank, taken along the line 7-7 of FIG. 1, and shown with thetwo-piece retainer shown in cross-section as in FIG. 5 in an earlyassembly step according to the invention.

FIG. 8 is an enlarged cross-sectional view of the receiver, taken alongthe line 6-6 of FIG. 1, a partial front elevational view of the shank ofFIG. 1, and shown with the two-piece retainer shown in cross-section asin FIG. 5 in an intermediate assembly step.

FIG. 9 is an enlarged cross-sectional view of the receiver, taken alongthe line 6-6 of FIG. 1, a partial front elevational view of the shank ofFIG. 1, shown with the two-piece retainer shown in cross-section as inFIG. 5 being assembled with the shank, and a cross-sectional view of thecompression insert taken along the line 9-9 of FIG. 1 in an initialassembly step within the receiver.

FIG. 10 is an enlarged cross-sectional view of the receiver, taken alongthe line 6-6 of FIG. 1, a partial front elevational view of the shank ofFIG. 1 with hidden portions shown in phantom, shown assembled with thetwo-piece retainer of FIG. 1 in front elevation and the compressioninsert of FIG. 1 in front elevational and further shown with thelongitudinal connecting member and closure top of FIG. 1 with portionsbroken away to show the detail thereof.

FIG. 11 is an enlarged and partial view similar to FIG. 10 furthershowing a rotational extent of the shank and cooperating two-pieceretainer.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure. It is also noted that any reference tothe words top, bottom, up and down, and the like, in this applicationrefers to the alignment shown in the various drawings, as well as thenormal connotations applied to such devices, and is not intended torestrict positioning of the bone attachment structures in actual use.

With reference to FIGS. 1-11 the reference number 1 generally representsa polyaxial bone screw apparatus or assembly according to the presentinvention. The assembly 1 includes a shank 4, that further includes abody 6 integral with an upwardly extending upper portion or capturestructure 8 having a top end surface 46; a receiver 10; a two-piece orpart retainer structure 12 and a compression or pressure insert 14. Theshank 4, receiver 10, retainer structure 12 and pressure insert 14preferably are assembled prior to implantation of the shank body 6 intoa vertebra (not shown).

FIG. 1 further shows a closure structure 18 of the invention for biasinga longitudinal member such as a rod 21 against the pressure insert 14which engages the shank top end surface 46 and biases the lower retainerstructure 12 into fixed frictional contact with both the shank upperportion 8 and the receiver 10, so as to fix the longitudinal connectingmember 21 relative to the vertebra. The shank top end 46 is spaced abovethe retainer 12 and the retainer 12 is disposed between the shank upperportion 8 and the receiver 10 lower portion 60. The receiver 10 and theshank 4 cooperate in such a manner that the receiver 10 and the shank 4can be secured at any of a plurality of angles, articulations orrotational alignments relative to one another and within a selectedrange of angles both from side to side and from front to rear, to enableflexible or articulated engagement of the receiver 10 with the shank 4until both are locked or fixed relative to each other near the end of animplantation procedure.

The shank 4, best illustrated in FIGS. 1, 2, 3 and 7, is elongate, withthe shank body 6 having a helically wound bone implantable thread 24extending from near a neck 26 located adjacent to the upper portion orcapture structure 8, to a tip 28 of the body 6 and extending radiallyoutwardly therefrom. During use, the body 6 utilizing the thread 24 forgripping and advancement is implanted into a vertebra leading with thetip 28 and driven down into the vertebra with an installation or drivingtool (not shown), so as to be implanted in the vertebra to near the neck26, as more fully described in the paragraphs below. The shank 4 has anelongate axis of rotation generally identified by the reference letterA.

The neck 26 extends axially outward and upward from the shank body 6.The neck 26 may be of slightly reduced radius as compared to an adjacentupper end or top 32 of the body 6 where the thread 24 terminates.Further extending axially and outwardly from the neck 26 is the shankupper portion 8 that provides a connective or capture apparatus disposedat a distance from the upper end 32 and thus at a distance from avertebra when the body 6 is implanted in such vertebra.

The shank upper portion or capture structure 8 is configured forconnecting the shank 4 to the receiver 10 and capturing the shank upperportion structure in the receiver 10. In the embodiment shown, thestructure 8 includes a polyhedral formation, specifically apolyhedron-like structure, generally 38, having a first pair of opposedoblique surfaces 40 and a second pair of adjacent opposed obliquesurfaces 42, each of the surfaces 40 and 42 are generally in the shapeof an inverted isosceles trapezoid and extend from an annular seatingsurface 44 to an upper end or top curved surface 46. The top surface 46is substantially spherical or domed shaped and terminates at a narrowtop annular surface 47 that is perpendicular to the axis A. The annularsurface 44 is also substantially perpendicular to the axis A and thesurfaces 40 and 42 form an oblique angle with respect to the surface 44.The optional annular seating surface 44 partially defines a ledge havinga rim 48 and a substantially spherical lower surface 50 that extendsfrom the rim 48 to adjacent the neck 26. The term oblique is used hereinto describe the surfaces 40 and 42 that are slanted or inclined indirection or course or position neither parallel nor perpendicular norright-angular, with respect to the shank body 6, but otherwise may bedisposed at a variety of angles with respect to the axis A. Also, othergeometries are possible (e.g., conical). The oblique surfaces 40 and 42slope from the top surface 46 toward the axis A in a direction towardthe tip 28 of the shank body 6. A width of each of the surfaces 40 and42 adjacent to the seating surface 44 is smaller than a width of each ofthe surfaces 40 and 42 measured near the spherical surface 46.

The shank 4 further includes a tool engagement structure or inner drive52 formed in the surface 47. The illustrated drive 52 is a hex drive oraperture for engaging a hex-shaped driving tool (not shown) for bothdriving and rotating the shank body 6 into a vertebra. Other shapeddrives and cooperating tools are possible, such as grooved,multi-lobular, etc. While not required in accordance with practice ofthe invention, the surfaces 40, 42, 44 and 46 may be scored or knurledto further increase frictional engagement between such surfaces andcooperating surfaces of the retainer 12 and insert 14.

The shank 4 shown in the drawings is cannulated, having a small centralbore 54 extending an entire length of the shank 4 along the axis A fromthe internal drive 52 to the tip 28. The bore 54 is coaxial with thethreaded body 6. The bore 54 provides a passage through the shank 4interior for a length of wire (not shown) inserted into a vertebra priorto the insertion of the shank body 6, the wire providing a guide forinsertion of the shank body 6 into the vertebra 15.

To provide a biologically active interface with the bone, the threadedshank body 6 may be coated, perforated, made porous or otherwisetreated. The treatment may include, but is not limited to a plasma spraycoating or other type of coating of a metal or, for example, a calciumphosphate; or a roughening, perforation or indentation in the shanksurface, such as by sputtering, sand blasting or acid etching, thatallows for bony ingrowth or ongrowth.

Certain metal coatings act as a scaffold for bone ingrowth. Bio-ceramiccalcium phosphate coatings include, but are not limited to:alpha-tri-calcium phosphate and beta-tri-calcium phosphate (Ca₃(PO₄)₂,tetra-calcium phosphate (Ca₄P₂O₉), amorphous calcium phosphate andhydroxyapatite (Ca₁₀(PO₄)₆(OH)₂). Coating with hydroxyapatite, forexample, is desirable as hydroxyapatite is chemically similar to bonewith respect to mineral content and has been identified as beingbioactive and thus not only supportive of bone ingrowth, but activelytaking part in bone bonding.

With particular reference to FIGS. 1 and 6-11, the receiver 10 has agenerally U-shaped appearance with a discontinuous partially cylindricaland partially spherical inner profile and a partially curved andpartially faceted outer profile. The receiver has an axis of rotation Bthat is shown in FIG. 1 as being aligned with and the same as the axisof rotation A of the shank 4, such orientation being desirable duringassembly of the receiver 10 with the shank 4, the retainer pieces 12 andthe insert 14. After the receiver 10 is pivotally attached to the shank4, and the assembly 1 is implanted in a vertebra (not shown), the axis Bis typically disposed at an angle with respect to the axis A as shown inFIG. 11.

The receiver 10 includes a base 60 integral with a pair of opposedupstanding arms 62 forming a cradle and defining a U-shaped channel 64between the arms 62 with an upper opening, generally 66, and a lowerseat 68, the channel 64 having a width for operably snugly receiving therod 21 between the arms 62. Each of the arms 62 has an interior surface70 that defines the inner cylindrical profile and includes a partialhelically wound guide and advancement structure 72. In the illustratedembodiment, the guide and advancement structure 72 is a partialhelically wound interlocking flangeform configured to mate underrotation with a similar structure on the closure structure 18, asdescribed more fully below. However, it is foreseen that the guide andadvancement structure 72 could alternatively be a square-shaped thread,a buttress thread, a reverse angle thread or other thread like ornon-thread like helically wound discontinuous advancement structure foroperably guiding under rotation and advancing the closure structure 18downward between the arms 62, as well as eventual torquing when theclosure structure 18 abuts against the rod 21, or in some embodiments,an upper compression insert.

An opposed pair of tool receiving and engaging apertures 74 are formedon outer surfaces 76 of the arms 62. A pair of substantially cylindricalinner surfaces 78 define the apertures 74, with a portion of each of theapertures 74 extending through the arms 62 as illustrated, for example,in FIGS. 10 and 11. A pair of tabs 80, each having a lower end or bodyportion 82 integral with a respective arm 62 at a lower portion of oneof the cylindrical surfaces 78, and an upper end portion 84 extendingupwardly and, as shown in FIG. 11, also inwardly, from the respectivelower body portion 82, the tab 80 generally directed towards the guideand advancement structure 72 of the respective arm 62 and also towardthe axis B. An operational orientation of each of the tabs 80 is angledtoward the axis B with an inner surface or edge of the upper end portion84 in sliding engagement with a surface or slot in the cooperatinginsert 14 as will be described in greater detail below. The tabs 80 aretypically initially disposed parallel to the axis B as shown in FIG. 6,and then a tool (not shown) is inserted into the aperture 74 from theoutside surface 76 and engages and pushes a surface 86 of the tab 80 andbends the tab 80 inwardly in a direction toward the axis B until the tab80 is at the illustrated desired angular position. Such bending of thetabs 80 may be performed either prior to or after assembly of thereceiver 10 with the insert 14, the shank 4 and the retainer pieces 12.It is also foreseen that the tabs 80 may be machined or otherwisepre-fabricated to be angled or directed toward the axis B as is shown inthe drawing figures. In other embodiments of the invention, the tabs maybe integral with an upper portion of receiver near the aperture 74 andbe directed downwardly away from the guide and advancement structures72. The illustrated tabs 80 are resilient, having a spring-like nature.Thus, when operatively cooperating with the insert 14, the tabs 80 biasagainst the insert 14, holding such insert in a desired position and yetthe tabs 80 are flexible enough to allow a user to make desiredadjustments of the position of the insert 14 within the receiver 10.

Each of the illustrated receiver arms 62 may also include a V-shaped orundercut tool engagement groove (not shown), formed on outer surfaces 76thereof which may be used for holding the receiver 10 with a holdingtool (not shown) having projections that are received within suchgrooves during implantation of the shank body 6 and/or during subsequentinstallation of the rod 21 or other longitudinal connecting member andthe closure structure 18. It is foreseen that tool receiving grooves orapertures may be configured in a variety of shapes and sizes and bedisposed at other locations on the receiver arms 62.

Communicating with the U-shaped channel 64 of the receiver 10 is achamber or cavity 90 defined in part by a substantially cylindricalupper portion 92 and by a lower inner substantially spherical retainerseating surface 94 of the base 60. The upper portion 92 is located belowthe guide and advancement structures 72 and may include one or morecylindrical surfaces for sliding cooperation with an insert or inserts.The apertures 74 and the tabs 80 communicate with the cylindrical upperportion 92. The seating surface 94 is near or adjacent to thecylindrical portion 92. The seating surface 94 is sized and shaped forslidable mating and eventual frictional engagement with the retainerpieces 12, as described more fully below. The cavity 90 opens into theU-shaped channel 64 and also to a lower neck 96 defining a bore orcircular opening that communicates with a lower exterior 98 of the base60. The circular neck 96 is coaxially aligned with the rotational axis Bof the receiver 10. The neck 96 is sized and shaped to be smaller thanan outer radial dimension of the operationally assembled retainer pieces12, as will be discussed further below, so as to form a restriction atthe location of the neck relative to the retainer 12, to prevent theretainer 12 from passing from the cavity 90 and out to the lowerexterior 98 of the receiver 10 when the retainer 12 is seated andassembled about the shank upper portion 8.

The two-part retainer and articulation structure 12 is used to retainthe upper portion or capture structure 8 of the shank 4 within thereceiver 10 and articulate the shank body 6 with respect to the receiver10. The retainer pieces are each sized and shaped to frictionally engagethe shank upper portion while being pivotally mounted with respect tothe receiver, the pieces located below the top end surface 46 andbetween the shank upper portion and the receiver base 60 and beingarticulatable with respect to the receiver surface 94 until the shank 6is fixed in a desired position with respect to the receiver base 60. Theretainer structure 12, best illustrated in FIGS. 1, 4 and 5, has anoperational central axis that is the same as the elongate axis Aassociated with the shank 4. The structure 12 includes a first piece orpart 101 and an opposingly positioned, and in this embodiment asubstantially identical or mirror image second piece or part 102. Theparts 101 and 102 provide a collar about the upper portion 8, with thetop surface 46 of the portion 8 extending upwardly above the parts 101and 102 and towards the opening 66 within the receiver 10, and each ofthe parts 101 and 102 disposed between the portion 8 and the receiver 10when installed, as will be discussed more fully below. The parts orpieces 101 and 102 slidably and closely grip both the upper portion 8and the seating surface 94, providing an even and uniform grippingsurface between the shank 4 and the receiver 10 at the spherical seatingsurface 94 when force is directed onto the shank domed top surface 46 bythe insert 14 cooperating with the rod 21 and the closure structure 18,or by other types of longitudinal members, inserts and closurestructures.

Although a two-piece retainer structure 12 is illustrated herein, it isforeseen that the retainer structure may be made up of more than twopieces, each slidably frictionally matable with both the shank upperportion or capture structure 8 and the seating surface 94 of thereceiver 10. The pieces may also be of varying sizes and not necessarilymirror images of one another. The mating surfaces of the shank upperportion and cooperating retainer pieces may have greater or fewer planarsurfaces or may be curved, for example, conical in form. Additionally,it is foreseen that the pieces may include a plurality of planar orcurved surfaces, such as undulating or zig-zag surfaces, forming peaksand valleys that would cooperate and mate with similarly configuredsurfaces on the shank upper portion. Furthermore, although theillustrated embodiment shows the parts 101 and 102 in contact with eachother when fully installed in the receiver 10 and in contact with theshank upper portion 8, it is foreseen that the parts 101 and 102 may besized and shaped so as to be in spaced relation to one another whenfully installed with the shank upper portion 8 and within the receiver10.

Each retainer part 101 and 102 includes a substantially spherical outersurface, 104 and 105, respectively, each having a radius substantiallysimilar to a radius of the receiver seating surface 94. The parts 101and 102 further include respective planar top surfaces 107 and 108 andrespective planar bottom surfaces 110 and 111. The illustrated surface107 and the surface 110 are substantially parallel. The illustratedsurface 108 and the surface 111 are substantially parallel. The surfaces110 and 111 each abut and seat upon the annular seating surface 44 ofthe shank 4 when fully installed in the receiver 10 as shown in FIGS.9-11. Adjacent to the top surfaces 107 and 108 are respective slopingplanar surfaces 114 and 115. The surface 114 is adjacent to thespherical outer surface 104 and the surface 115 is adjacent to thespherical outer surface 105. As shown in FIG. 11, for example, thesurfaces 114 and 115 advantageously allow for clearance between theretainer 12 and the insert 14 when pivoting the shank 4 with respect tothe receiver 10 into a desired position.

With particular reference to FIG. 2, each of the retainer structureparts 101 and 102 have a squared-off U-shape or C-shape, when viewedfrom the top or bottom, with planar, sloping surfaces formed about aspace or passage sized and shaped to mate with the surfaces 40 and 42 ofthe shank upper portion 8. With particular reference to FIG. 4, the part101 includes sloping inner planar surfaces 118, 119 and 120 and the part102 includes adjacent inner sloping planar surfaces 122, 123 and 124.When the retainer structure parts 101 and 102 are operationally disposedin the receiver 10 with the substantially spherical surfaces 104 and 105in frictional contact with the spherical seating surface 94, and thebottom surfaces 110 and 111 are seated on the annular seating surface44, which in some embodiments is not needed, of the shank upper portion8, the surfaces 118, 119, 120, 122, 123 and 124 are disposed at a degreeof inclination with respect to the bottom surfaces 110 and 111,respectively, corresponding or congruent to a degree of inclination ofthe side surfaces 40 and 42 of the upper portion 8 with respect to theseating surface 44, such that substantially full frictional contact ismade between at least one of the opposed pair surfaces 40 or 42 with thesurfaces 119 and 123 of the respective parts 101 and 102 with thesurfaces 118, 120, 122 and 124 being in slidable contact with the otherpair of opposed surfaces 40 or 42. Once in full operational assembly andlocked into place, preferably all the surfaces 118, 119, 120, 122, 123and 124 are in full or at least partial frictional engagement with oneof the surfaces 40 and 42. It is noted that because the parts 101 and102 are substantially identical and mirror images of each other, and thesurfaces 40 and 42 of the shank upper portion also are substantiallyidentical, the retainer structure functions equally well with the slopedsurfaces 118, 119, 120, 122, 123 and 124 in contact with either of thesurfaces 40 and 42 of the shank upper portion 8. Although theillustrated walls or surfaces 40, 42, 118, 119, 120, 122, 123 and 124are illustrated as smooth and planar, it is foreseen that these surfacesmay be roughened or abraded to provide enhanced frictional contactbetween the retainer pieces 101 and 102 and the shank upper portion 8.Furthermore, the outer surfaces 104 and 105 of the retainer andarticulation structure 12 that contact the substantially sphericalseating surface 94 of the receiver may also be a high friction surface,such as a knurled surface.

The retainer part or piece 101 further includes end walls 132 and 133,extending from the outer surface 104 to the inner walls 118 and 120,respectively. The end walls 132 and 133 are disposed substantiallyperpendicular to the bottom surface 110. The retainer part 102 furtherincludes end walls 134 and 135, extending from the outer surface 105 tothe inner walls 122 and 124, respectively. The end walls 134 and 135 aredisposed substantially perpendicular to the bottom surface 111. Each ofthe walls 132, 133, 134 and 135 include a top bevel 136. The retainerparts 101 and 102 are configured such that, when operationally disposedin the receiver 10, with the substantially spherical surfaces 104 and105 in sliding frictional contact with the spherical seating surface 94,and with the bottom surfaces 110 and 111 seated on the annular seatingsurface 44 of the shank 4, the end walls 132 and 133 are in contact withthe respective end walls 134 and 135, as illustrated in FIGS. 1 and 4.The bevels 136 providing clearance space for installing the retainerstructure parts 101 and 102 about the capture structure 8 within thereceiver 10 in a method of the invention described subsequently herein.It is foreseen that also in accordance with the invention, to provideadditional clearance during installation, the parts 101 and 102 may beconfigured such that the end walls 132 and 133 are in spaced,substantially parallel relation with the respective end walls 134 and135, when fully installed in the bone screw receiver 10.

With particular reference to FIGS. 1 and 9-11, the illustratedcompression insert 14 is sized and shaped to be received by anddownloaded into the receiver 10 at the upper opening 66. However, inother embodiments of the invention, the insert 14 may be sized foruploading or downloading into the receiver 10. In operation, the insert14 is disposed between the rod 21 and the upper portion 8 of the bonescrew shank 4 as illustrated for example in FIGS. 10 and 11. When theclosure structure 18 presses upon the rod 21, the rod 21 operativelypresses upon the insert 14 that in turn presses upon the shank top endsurface 46, that in turn causes the shank upper portion 8 to pressagainst the retainer pieces 12 that in turn press against the seatingsurface 94 of the receiver 10, resulting in ultimate frictionalengagement and locking of the angular position of the bone screw shank 4with respect to the receiver 10. The compression insert 14 has anoperational central axis that is the same as the central axis B of thereceiver 10.

The compression insert 14 has a central channel or through boresubstantially defined by an inner cylindrical surface 141 coaxial withan inner partially spherical surface 142. The compression insert 14through bore is sized and shaped to receive a driving tool (not shown)therethrough that engages the shank drive feature 52 when the shank body6 is driven into bone. The surface 142 is sized and shaped to cooperateand ultimately frictionally engage the substantially spherical or domedsurface 46 of the shank upper portion 8 such that the surface 142initially slidingly and pivotally mates with the spherical surface 46.The surface 142 may include a roughening or surface finish to aid infrictional contact between the surface 142 and the surface 46, once adesired angle of articulation of the shank 4 with respect to thereceiver 10 is reached.

The compression insert 14 also includes a pair of arms 144 with aU-shaped surface or saddle 146 formed therebetween. The saddle 146defines a U-shaped channel that communicates with the bore defined bythe cylindrical surface 141 and the spherical surface 142. The curvedsurface or saddle 146 is sized and shaped to closely receive thecylindrical rod 21 or other longitudinal connecting member. The saddle146 extends from top surfaces 148 of the arms to a curved lower seat 150located near a bottom surface 152 of the insert 14. The surface 152slopes upwardly from and communicates with the inner spherical surface142, the surface 152 allowing for clearance between the insert 14 andthe retainer pieces 12 as best shown in FIG. 11. The height of the arms144 can vary as can their thickness and the area for their top surfaces148.

In operation, the lower seat 150 (as well as a substantial portion of aremainder of the saddle 146) frictionally engages an outer surface 22 ofthe rod 21. A base having an outer cylindrical surface 154 is disposedbetween the saddle 146 and the bottom surface 152. The cylindricalsurface 154 also extends upwardly about the arms 144. Formed in thesurface 154 and located centrally with respect to each arm 144 is ashallow groove or depression 156. Each illustrated groove 156 issubstantially U-shaped and runs from the respective top surface 148 to acurved or flat bottom 158 located approximately centrally between thetop surface 148 and the bottom surface 152. The grooves 156 are sizedand shaped to cooperate with the tabs 80 of the receiver 10 as will bedescribed in greater detail below. The grooves 156 may be of any shapeand are preferably elongate, running parallel to a central axis of theinsert 14 that is operationally coaxial with the axis B of the receiver10, and have a width that receives the respective tab 80 within suchgroove. In the illustrated embodiment, the grooves or depressions 156are substantially flat surfaces formed by planing the cylindricalsurface 154. The compression or pressure insert 14 ultimately seats onthe shank upper portion 8 and is disposed substantially in the uppercylindrical portion 92 of the cavity 90, with the tabs 80 holding theinsert 14 in desired alignment with respect to the rod 21 as will bedescribed in greater detail below. In operation, the insert 14 extendsat least partially in the channel 64 such that the saddle 146 surfacesubstantially contacts and engages the outer surface 22 of the rod 21when such rod is placed in the receiver 10 and the closure structure ortop 18 is tightened thereon.

The elongate rod or longitudinal connecting member 21 that is utilizedwith the assembly 1 can be any of a variety of implants utilized inreconstructive spinal surgery, but is typically a cylindrical, elongatestructure having the outer substantially smooth, cylindrical surface 22of uniform diameter. The rod 21 may be made from a variety of metals,metal alloys and deformable and less compressible plastics, including,but not limited to rods made of elastomeric, polyetheretherketone (PEEK)and other types of materials. The rod 21 is cradled by and directly orabutingly engages the insert 14 at the saddle 146, as shown in FIGS. 10and 11 and is biased against the saddle 146 by pressure from the closurestructure 18, consequently biasing the insert surface 142 against theshank upper portion top end surface 46, pressing the shank 4 downwardlyin a direction toward the base 60 of the receiver 10 when the assembly 1is fully assembled. The shank 4 and retainer structure pieces 12 arethereby locked or held in position relative to the receiver 10 by therod 21 firmly pushing downward on the insert 14 that in turn pushes downon the shank upper surface 46.

With reference to FIGS. 1, 10 and 11, the closure structure or closuretop 18 can be any of a variety of different types of closure structuresfor use in conjunction with the present invention with suitable matingstructure on the upstanding arms 62. In the embodiment shown, theclosure top 18 is rotatably received between the spaced arms 62, butcould be a slide-in closure structure. The illustrated closure structure18 is substantially cylindrical and includes an outer helically woundguide and advancement structure 162 in the form of a flange form thatoperably joins with the guide and advancement structure 72 disposed onthe arms 62 of the receiver 10. The flange form utilized in accordancewith the present invention may take a variety of forms, including thosedescribed in Applicant's U.S. Pat. No. 6,726,689, which is incorporatedherein by reference. It is also foreseen that according to the inventionthe closure structure guide and advancement structure couldalternatively be a buttress thread, a square thread, a reverse anglethread or other thread like or non-thread like helically woundadvancement structure for operably guiding under rotation and advancingthe closure structure 18 downward between the arms 62 and having such anature as to resist splaying of the arms 62 when the closure structure18 is advanced into the U-shaped channel 64. The illustrated closurestructure 18 also includes a top surface 164 with an internal drive 166in the form of an aperture that is illustrated as a hex drive, or maybe, for example, a star-shaped internal drive such as that sold underthe trademark TORX, or other internal drives such as slotted, tri-wing,spanner, two or more apertures of various shapes, and the like. Adriving tool (not shown) sized and shaped for engagement with theinternal drive 166 is used for both rotatable engagement and, if needed,disengagement of the closure 18 from the receiver arms 62. It is alsoforeseen that the closure structure 18 may alternatively include abreak-off head designed to allow such a head to break from a base of theclosure at a preselected torque, for example, 70 to 140 inch pounds.Such a closure structure would also include a base having an internaldrive to be used for closure removal. A bottom surface 168 of theclosure may be planar or include a point, points, a rim or rougheningfor engagement with the surface 22 of the rod 21. The closure top 18 mayfurther include a cannulation through bore (not shown) extending along acentral axis thereof and through the top and bottom surfaces thereof.Such a through bore provides a passage through the closure 18 interiorfor a length of wire (not shown) inserted therein to provide a guide forinsertion of the closure top into the receiver arms 62.

Prior to the polyaxial bone screw assembly 1 being placed in useaccording to the invention, the retainer structure pieces 101 and 102are typically first inserted or top-loaded into the receiver U-shapedchannel 64 at the opening 66, as shown in FIG. 6, and then into thecavity 90 to ultimately dispose the structure pieces 12 adjacent to theinner surface 94 of the receiver 10. Alternatively, one of the retainerstructure pieces 101 may be inserted or top-loaded into the channel 64at the opening 66, while the other retainer structure piece 102, mayinserted or bottom-loaded into the cavity 90 at the lower neck 96.Alternatively, both pieces 101 and 102 may be uploaded at the neck 96.

With reference to FIGS. 7 and 8, after the retainer pieces 101 and 102are disposed in the cavity 90, the shank 4 is inserted or up-loaded intothe receiver 10 at the neck 96. With particular reference to FIG. 8, thesloping surfaces 40 and 42 of the shank upper portion 8 come intocontact with the sloping inner surfaces 118, 119, 120, 122, 123 and 124of the respective retainer pieces 101 and 102. Initially all threecomponents, the shank upper portion 8, and the pieces 101 and 102 maymove upwardly into the cavity 90. As the shank upper portion 8 continuesto move upwardly and into the cavity 90, the retainer structure pieces101 and 102 pivot about edges thereof and then begin to move downwardlytoward the base 60 until in operational alignment as shown in FIG. 9with the bottom surfaces 110 and 111 abutting and seated upon theannular seating surface 44 of the shank 4. Once seated upon the annularsurface 44, the retainer structure sloping surfaces 118, 119, 120, 122,123 and 124 frictionally engage the capture structure side surfaces 40and 42. Subsequent slight downward movement (directed away from the topopening 66) by the shank 4, as well as the frictionally engaged retainerpieces 101 and 102, seats the shank/retainer structure assembly in thereceiver cavity 90, with the retainer outer spherical surfaces 104 and105 in sliding engagement with the receiver seating surface 94. Theretainer structure pieces 12, now fully seated in the receiver 10 arecoaxially aligned with the shank upper portion. At this time, the shankupper portion 8, the retainer structure 12, the receiver seating surface94 and the lower aperture or neck 96 cooperate to maintain the shankbody 6 in pivotal and rotational relation with the receiver 10. Only theretainer structure 12 is in slidable engagement with the receiverspherical seating surface 94. Both the shank upper portion 8 and thethreaded portion of the shank body 6 are in spaced relation with thereceiver 10. An extent of rotation is shown in FIG. 11 where it isillustrated that the shank body 6 can be rotated through a substantialangular rotation relative to the receiver 10, both from side to side andfrom front to rear so as to substantially provide a universal or balljoint wherein the angle of rotation is only restricted by engagement ofthe neck of the shank body 6 with the restrictive neck 96 of thereceiver 10.

Prior to the polyaxial bone screw assembly 1 being placed in useaccording to the invention the tabs 80 of the receiver 10 may be bentinwardly toward the axis B as shown in FIGS. 11. This is accomplished byinserting an elongate tool (not shown) into each of the toolingapertures 74 and pressing the respective tab 80 inwardly toward the axisB until the tab end 84 is disposed at least partially within the uppercylindrical portion 92 of the cavity 90. In the illustrated embodiment,the insert 14 is top loaded through the opening 66 of the receiver 10and the grooves 156 are aligned with the tabs 80. The tabs 80 are bentinwardly toward the axis B after the pressure insert 14 is located inthe cylindrical portion 92 of the cavity 90. The tabs 80 are thenpressed toward the axis B until the tabs 80 come into frictionalengagement with surfaces 156 of the receiver 14. The tabs 80 pressagainst the insert 14 at the grooves 156, allowing for some upward anddownward adjustment of the insert 14. However, rotation of the insert 14about the axis B is prohibited by the tabs 80 abutting against surfacesforming the grooves 156.

The retainer 12 and the attached shank upper portion 8 may then bemanipulated into a substantially coaxial position with the insert 14 inreadiness for bone implantation. The assembly 1 is typically screwedinto a bone, such as a vertebra (not shown), by rotation of the shank 4using a driving tool (not shown) that operably drives and rotates theshank 4 by engagement thereof with the drive feature 52.

The vertebra (not shown) may be pre-drilled to minimize stressing thebone and have a guide wire (not shown) inserted to provide a guide forthe placement and angle of the shank 4 with respect to the vertebra. Afurther tap hole may be made using a tap with the guide wire as a guide.Then, the bone screw assembly 1 is threaded onto the guide wireutilizing the cannulation bore 54 by first threading the wire into theopening at the bottom 28 and then out of the top opening at the drivefeature 52. The shank 4 is then driven into the vertebra using the wireas a placement guide. It is foreseen that the bone screw assemblies 1,the rod 21 (also having a central lumen in some embodiments) and theclosure top 18 (also with a central bore) can be inserted in apercutaneous or minimally invasive surgical manner, utilizing guidewires.

With reference to FIG. 10, the rod 21 is eventually positioned in anopen or percutaneous manner in cooperation with the at least two bonescrew assemblies 1. Alignment of the rod surface 22 with the saddle 146of the insert 14 is initially provided and then maintained by pressureplaced at the insert grooves 156 by the tabs 80. The closure structure18 is then inserted into and advanced between the arms 62 of each of thebone screw assemblies 1. The closure structure 18 is rotated, using atool engaged with the inner drive 166 until a selected pressure isreached at which point the rod 21 engages the saddle 146 and the rod isurged toward, but not in contact with the lower seat of the receiver 10that defines the U-shaped channel 64. For example, about 80 to about 120inch pounds pressure may be required for fixing the bone screw shank 6with respect to the receiver 10.

As the closure structure 18 rotates and moves downwardly into therespective receiver 10, the bottom surface 168 presses against the rodsurface 22, biasing the rod into engagement with the compression insert14 that operably produces a frictional engagement between the insertsurface 142 and the shank surface 46 and also urges the shank upperportion 8 toward the retainer 12 and, in turn, the structure 12 in adirection toward the base 60 of the receiver 10, so as to frictionallyseat the spherical surfaces 104 and 105 against the internal sphericalseating surface 94 of the receiver 10, also fixing the shank 4 and theretainer 12 in a selected, rigid position relative to the receiver 10.At this time it is also possible for the retainer 12 to expand somewhatfor an even tighter fit in the receiver cavity lower seat 94.

If removal of the rod 21 from any of the bone screw assemblies 1 isnecessary, or if it is desired to release the rod 21 at a particularlocation, disassembly is accomplished by using the driving tool (notshown) that mates with the internal drive 166 on the closure structure18 to rotate and remove the closure structure 18 from the cooperatingreceiver 10. Disassembly is then accomplished in reverse order to theprocedure described previously herein for assembly.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

What is claimed and desired to be secured by Letters Patent is asfollows:
 1. A bone anchor assembly comprising: a) a bone attachmentstructure having an integral upper capture portion and a lower threadedportion for fixation in a bone; b) a receiver having an inner cavity anda lower opening through which the bone attachment structure can pivotwith respect to the receiver; the inner cavity operably receiving theupper capture portion and having an interior surface; and c) a retainerstructure being positioned within the receiver cavity prior to the boneattachment structure and having at least two discrete parts, each parthaving an upper capture portion engaging inner surface and a receivercavity engaging outer surface, the inner surfaces configured to becomeinto mating contact with the upper capture portion within the receivercavity, so as to maintain the upper capture portion in the receiver, andwherein the outer surfaces are configured to be in slidable engagementwith the cavity interior surface when the retainer structure is locatedin the receiver between the bone attachment structure and the cavityinterior surface.
 2. The assembly of claim 1, including a compressioninsert disposed within the receiver to frictionally engage the boneattachment structure.
 3. The assembly of claim 1, wherein the boneattachment structure upper capture portion extends above the retainerstructure.
 4. The assembly of claim 1, wherein each retainer structurepart outer surface and the cavity interior surface are partiallyspherical in shape.
 5. The assembly of claim 1, wherein the boneattachment structure upper capture portion is uploaded into the cavitythrough the opening.
 6. The assembly of claim 2, wherein the boneattachment structure upper capture portion extends above the retainerstructure.
 7. A bone anchor assembly comprising: a) a receiver having anupper portion integral with a base, the upper portion defining arod-receiving channel therein, the base including a bottom openingcommunicating with an internal cavity, the cavity having a surface; b) ashank having a lower bone attachment structure and an integral uppercapture structure up-loadable into the cavity through the receiverbottom opening; and c) a retainer structure having at least two discreteparts, each part with a top and bottom surface and being pre-disposed inthe cavity of the receiver before the shank is up-loaded; and whereinthe two discrete parts capture the shank in the receiver at the shankupper capture structure such that the shank is then pivotable withrespect to the receiver, and the two discrete parts form a plurality ofspaces between the parts that extend from the top to the bottom surfacesthereof with respect to each part.
 8. The bone anchor assembly of claim7, wherein the two discrete parts rotate while slidably engaging thereceiver cavity surface when capturing the shank capture structure. 9.The bone anchor assembly of claim 7, wherein the shank is bottom-loaded.10. The bone anchor assembly of claim 7, wherein the shank has polyaxialmotion with respect to the receiver.
 11. The bone anchor assembly ofclaim 7, wherein the two discrete parts pivot with respect to the shank.12. The bone anchor assembly of claim 7, wherein the shank upper capturestructure extends above each of the retainer discrete parts.
 13. Thebone anchor assembly of claim 7, wherein the two discrete parts moveaway from each other while slidably engaging the receiver cavitysurface, so as to capture the shank capture structure.
 14. The boneanchor assembly of claim 7, wherein the shank further includes anannular seating surface.
 15. A bone anchor assembly comprising: a) areceiver including an upper portion having a rod-receiving channel andan integral base with a lower opening communicating with an internalcavity, the cavity having a cavity surface; b) a shank having a distalbone attachment portion and a proximal capture portion; c) a retainerstructure including at least two discrete parts, each part having anouter surface and an internal surface that engages the shank proximalcapture portion; and wherein the outer surface of the retainer structureis in slidable engagement with the cavity surface of the receiver andthe internal surface captures the shank capture portion, such that theshank pivots with respect to the receiver.
 16. The bone anchor assemblyof claim 15, wherein the two discrete parts rotate while slidablyengaging the receiver cavity surface when capturing the shank proximalcapture structure.
 17. The bone anchor assembly of claim 15, wherein theshank is bottom-loaded.
 18. The bone anchor assembly of claim 15,wherein the shank has polyaxial motion with respect to the receiver. 19.The bone anchor assembly of claim 15, wherein the two discrete partspivot with respect to the shank.
 20. The bone anchor assembly of claim15, wherein the shank proximal capture structure extends above each ofthe retainer discrete parts.
 21. The bone anchor assembly of claim 15,wherein the two discrete parts move away from each other while slidablyengaging the receiver cavity surface, so as to capture the shankproximal capture portion.
 22. The bone anchor assembly of claim 15,wherein the shank further includes an annular seating surface.
 23. Abone anchor assembly comprising: a) a receiver having an upper portionand base, the upper portion defining a rod-receiving channel therein,the base including a bottom opening communicating with an internalcavity, the cavity having a cavity surface; b) a shank having a lowerbone attachment structure and an upper capture structure up-loadableinto the cavity through the receiver bottom opening; c) a retainerstructure having at least two discrete parts, each part being positionedwithin the cavity and substantially below the rod-receiving channel inthe cavity and in slideable engagement with the cavity surface, prior tothe shank being up-loaded; and wherein the two discrete parts mate tocapture the shank in the receiver at the shank upper capture structuresuch that the shank is then pivotable with respect to the receiver andprevented from coming out of the receiver bottom opening.
 24. A boneanchor assembly comprising: a) a shank having an elongate body includingan upper capture portion and a lower threaded portion for fixation in abone that are integral with the elongate body; b) a receiver having abody including an upper portion and a lower portion integral with thebody, and an inner cavity operably receiving the shank upper captureportion and having an interior surface; the receiver including a loweropening through which the shank can pivot with respect to the receiver;and c) a retainer structure being positioned within the receiver cavityprior to the shank and having at least two discrete parts, each parthaving a shank engaging inner surface and a receiver cavity engagingouter surface, the inner surfaces configured to become into matingcontact with the shank upper capture portion within the receiver cavity,so as to maintain the shank upper capture portion in the receiver, eachpart cooperating to prevent the shank from coming out of the loweropening, and wherein the outer surfaces are configured to be in slidableengagement with the cavity interior surface when the retainer structureis located in the receiver between the shank upper capture portion andthe cavity interior surface, the retainer structure at least partiallysurrounding the shank upper capture portion.
 25. A bone anchor assemblycomprising: a) a bone attachment structure having an integral uppercapture portion and a lower portion for fixation in a bone; b) areceiver having an inner cavity and a lower opening through which thebone attachment structure can pivot with respect to the receiver; theinner cavity operably receiving the upper capture portion and having aninterior surface; and c) a retainer structure being positioned withinthe receiver cavity prior to the bone attachment structure and having atleast two discrete parts, each part having an upper capture portionengaging inner surface and a receiver cavity engaging outer surface, theinner surfaces configured to become into mating contact with the uppercapture portion within the receiver cavity, so as to maintain the uppercapture portion in the receiver, and wherein the retainer structure islocated in the receiver between the bone attachment structure and thecavity interior surface, so as to prevent the bone attachment structurefrom exiting the receiver lower opening.
 26. A bone anchor assemblycomprising: a) a receiver having an upper portion and base, the upperportion defining a rod-receiving channel therein, the base including abottom opening communicating with an internal cavity, the cavity havinga cavity surface; b) a shank having a lower bone attachment structureand an upper capture structure up-loadable into the cavity through thereceiver bottom opening; c) a retainer structure having at least twodiscrete parts, each part being positioned within the cavity andmoveable with respect to each other and with respect to the cavitysurface, prior to the shank being up-loaded; and wherein the twodiscrete parts mate to capture the shank in the receiver at the shankupper capture structure such that the shank is then pivotable withrespect to the receiver and prevented from coming out of the receiverbottom opening.